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RuneLancer

Curious about something...

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I'm somewhat curious about this. Would having one big poly affect performance negatively? Assuming, for instance, I'm rendering a large static background image - should I break it up into a mesh of X by X quads instead of rendering a large full-screen quad?

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Having a big poly could affect performance negatively, yes. It would eat up fill rate. However, breaking it up into sub meshes would only make things worse because not only would it eat up fill rate, but it would eat up extra vertex processing too. So my advice to you would simply be, use the big poly if you have to, but definitely DONT break it up into smaller quads. (There may be some optimizations I don't know of, that would tip the scales the other way, but i sincerely doubt it)

cheers
-Dan

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Guest Anonymous Poster
It probably doesn't apply in this case, but different platforms respond in different ways to different geometry. I seem to recall that the ps2 caches tiles of vram, and that having polys that are wider than the tile cache will thrash the cache, but tall thin polys play friendly. On a ps2 it would be beneficial to draw the background image in a series of thin vertical rectangles.

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If you're planning to cover the entire screen, just use a single polygon. Fill rate for the entire screen is expensive, so if you plan to use transparency, only do blending where you absolutely need to.

Bear in mind that if you intend to also do lighting on it as well, four vertices won't give you a very nice effect. In that case you will have to split it up into multiple polygons to increase the detail of the lighting.

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Well, here's what I'm doing: I'm using this big quad to render a background image. In fact I can have multiple "backgrounds" (such as a mesh of branches, vines, and leaves acting as a foreground in a forest setting, for instance, or multiple layers of clouds parallaxed together.)

Lighting isn't an issue - it's billboarded and I precalculate the colors to give all of my billboarded actors only once. It's essentially just one big textured billboarded quad.

I render it last, so I would guess the fill rate isn't TOO bad (the map already covers most of the screen) but if I can strip away some quads through an occlusion test, I'm not sure wether I'd see a performance boost or not.

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